1. Field of the Invention
This invention relates generally to solar cells and, in one particular embodiment, to an amorphous silicon thin film solar cell having improved haze characteristics.
2. Technical Considerations
A conventional amorphous silicon thin film solar cell typically includes a glass substrate over which is provided a transparent conductive oxide (TCO) contact layer and an amorphous silicon thin film active layer having a p-n junction. A rear metallic layer acts as a reflector and back contact. The TCO has an irregular surface to increase light scattering. In solar cells, light scattering or “haze” is used to trap light in the active region of the cell. The more light that is trapped in the cell, the higher the efficiency that can be obtained. However, the haze cannot be so great as to adversely impact upon the transparency of light through the TCO. Therefore, light trapping is an important issue when trying to improve the efficiency of solar cells and is particularly important in thin film cell design. However, with thin film devices, this light trapping is more difficult because the layer thicknesses are much thinner than those in previously know monocrystalline devices. As the film thicknesses are reduced, they tend toward coatings having predominantly parallel surfaces. Such parallel surfaces typically do not provide significant light scattering. This is particularly evident with coatings deposited by conventional chemical vapor deposition (CVD) coating methods. While conventional CVD coating methods provide advantages in throughput and cost, conventional CVD deposition tends to form smooth, uniform coating layers with a haze of less than 0.5% on a substrate. Such smooth coating layers do not typically provide layers having sufficient light scattering to significantly increase the efficiency of the solar cell.
Therefore, it would be desirable to provide a solar cell and a method of making the solar cell, particularly by a CVD method, having improved light scattering characteristics.